1. Field of the Invention
The present invention relates to a process for the cleaning in turbulent flow regime of wellbore wall or tubing or casing. The present invention particularly relates to a process for the cleaning in turbulent flow regime of wellbore wall or tubing or casing using aqueous surfactant compositions.
2. Background of the Invention
An effective cleanout operation is important during drilling or workover of an oil or gas well, or for an acidizing treatment of a geological formation, or to secure the establishment of an effective bond between a cement composition and a wellbore wall or tubing or casing, in order to avoid undesirable results in oil and gas well operations. This is because, by way of example, an ineffective cleanout operation during drilling or workover of an oil well can result in damage where contamination and even plugging occurs at the formation from which there is intention to produce fluids.
Similarly, where an acidizing treatment of a formation is intended to increase the productivity of the formation, in the case that oil based contaminants are not removed from the wellbore zone adjacent to the formation interval, there can be a reduction in the effectiveness of the acidizing treatment. Moreover, poor cleaning of the wellbore wall, casing, liner or tubing string, can reduce the quality of the cement bonding during cementing operations, and therefore permit undesirable flow of fluids along the wellbore, or undesirable interconnection between separate formations zones, or undesirable fluid flow around the casing, or a failure to stabilize the casing in the wellbore. Remedial action for any of the above-mentioned problems, or resulting contamination of a formation interval, can incur substantial costs in both onshore and offshore well operations.
Foxenberg et al., describe in Hart""s Petroleum Engineer International, October 1998, p23-28, that for cleaning regimes where a cleaning agent flows over a surface to be cleaned such as the displacement of a drilling fluid with a spacer fluid, turbulent flow usually has the advantage of increasing the cleaning efficiency. To promote a turbulent flow regime, those skilled in the art normally use commercially available cleaning agents, diluted with locally available water, which is viscosified by addition of suitable polysaccharide-based, or other, viscosifiers.
In recent years alkylpolyglycoside-based surfactants have increased in importance because they are made from renewable raw materials, they have an excellent environmental profile and their excellent surfactant properties. They have become especially important in detergent compositions, primarily for household cleaning products. Anionic derivatives of alkylpolyglycosides are known in literature, e.g. from EP 510564 and EP 510565. The advantages of alkylpolyglycoside-based surfactants have led to their use in other fields; WO 0069261, e.g., describes their application in compositions for agrochemical preparations. Synergism between the alkylpolyglycosides and the anionic surfactants is commonly exploited in the personal care and detergent sectors.
In practice, some weight ratios of binary mixtures of alkylpolyglycosides with anionic surfactants show synergic behavior for some fundamental surfactant properties, such as lowering critical micelle concentration, interfacial tension, and the like, for some important applicative parameters including increases in foaming, wetting, dishwashing performance, and the like. The use of combinations of alkylpolyglycosides with traditional (non alkylpolyglycoside-based) anionic surfactants are widely described, as reviewed by Fabry, et al., in Happi (August 1994 p, 111-115). It is possible to find descriptions of many compositions and processes related to the use of alkylpolyglycoside-based surfactants for well bore cleaning. For example, the following U.S. Pat. Nos. 5,977,032, 5,996,692, and 6,112,814 all disclose such applications.
Solutions of alkylpolyglycoside based synergic surfactant mixtures are effective in removing water and oil based drilling fluids, thread sealant and lubricating materials and oil based contaminants commonly found in wellbores; these include diesel oil, mineral oil, synthetic oils and crude oil and naturally occurring hydrocarbon substances. Alkylpolyglycoside based surfactant mixtures can be used as wetting, dispersing and/or emulsifying agents in caustic environments, such as in contact with cement slurries, remaining surface active at relatively high pH.
Chan, in U.S. Pat. No. 5,458,197, suggested the use of traditional anionics as cosurfactants in alkylpolyglycoside cleaning compositions for oil and gas well operations, but does not mention the use of the anionic derivatives of alkylpolyglycosides.
Notwithstanding the improvements in well cleanout operations described in these patents, there continues to be a need to provide a cleanout composition which maintains or improves on the characteristics needed for cleaning and that has improved toxicological and environmental properties, in line with legislation governing the use of chemicals in the oil and gas industry, and especially for offshore operations.
In one aspect, the present invention is a process for cleaning a wellbore wall, tubing or casing using a turbulent flow regime characterized by: (a) preparing an aqueous surfactant composition containing from about 10% to 60% by weight of a mixture of surfactants, the mixture comprising from 10% to 50% by weight of an anionic derivative of an alkylpolyglycoside, from 35% to 80% by weight of an alkylpolyglycoside and from 5% to 25% by weight of an anionic derivative of a fatty alcohol, their balance being 100%; (b) diluting the aqueous surfactant composition in water to form a diluted aqueous surfactant composition and injecting the diluted aqueous surfactant composition into a wellbore containing drilling mud, oily residues or other undesirable deposits; (c) extracting from the wellbore the diluted aqueous surfactant composition containing the drilling mud, oily residues or other undesirable deposits; (d) removing the drilling mud, oily residues or other undesirable deposits from the diluted aqueous surfactant composition; and (e) optionally, re-using the diluted aqueous surfactant composition.
In another aspect, the present invention is an aqueous surfactant composition for use in cleaning wellbore walls, tubing or casings comprising (a) from about 10% to 60% by weight of a mixture of surfactants, the mixture comprising from 10% to 50% by weight of an anionic derivative of an alkylpolyglycoside, (b) from 35% to 80% by weight of an alkylpolyglycoside and (c) from 5% to 25% by weight of an anionic derivative of a fatty alcohol, their balance being 100%.
In still another aspect, the present invention is a process for the preparation of these aqueous surfactant compositions characterized by: (a) reacting at 110-130xc2x0 C. for about 2-3 hours a reducing saccharide with a fatty alcohol, the alcohol being in a 2 to 5 fold molar excess, forming a reaction mixture; (b) distilling off from the reaction mixture part of the unreacted fatty alcohol thus obtaining a mixture of alkylpolyglycoside and fatty alcohol containing from 3% to 15% of fatty alcohol; (c) esterifying the mixture of alkylpolyglycoside and fatty alcohol by adding to the mixture of alkylpolyglycoside and fatty alcohol at 110-130xc2x0 C. over a period of 15-240 minutes a bi- or tri-carboxylic acid selected from the group consisting of citric acid, tartaric acid, malic acid, maleic acid, and mixtures thereof, forming an esterified mixture of alkylpolyglycoside and fatty alcohol; (d) diluting the esterified mixture of alkylpolyglycoside and fatty alcohol with water; and (e) neutralizing the resulting product.
In another aspect, the present invention is a process for the preparation of these aqueous surfactant compostions, characterized by to (a) reacting at 110-130xc2x0 C. for about 2-3 hours a reducing saccharide with a fatty alcohol, the fatty alcohol being in a 2 to 5 fold molar excess, forming a reaction mixture; (b) distilling off from the reaction mixture part of the unreacted fatty alcohol thus obtaining a mixture of alkylpolyglycoside and fatty alcohol containing from 3% to 15% of fatty alcohol; (c) esterifying the mixture of alkylpolyglycoside and fatty alcohol by adding maleic anhydride to the mixture of alkylpolyglycoside and fatty alcohol at 110-130xc2x0 C. over a period of 15-240 minutes; (d) diluting the esterified mixture of alkylpolyglycoside and fatty alcohol with water; and (e) sulfonating the resulting mixture.
In the preferred embodiment of the present invention the total concentration of surfactants in the aqueous surfactant composition is about 20% to 50% by weight and the mixture of surfactants comprises from 15% to 45% by weight of an anionic derivative of an alkylpolyglycoside, from 40% to 75% by weight of an alkylpolyglycoside and from 8% to 15% by weight of an anionic derivative of a fatty alcohol, their balance being 100%. Respectively, the anionic derivative of an alkylpolyglycoside, the alkylpolyglycoside and the anionic derivative of fatty alcohol of the present invention are compounds represented by the formulae I, II and III:
where:
R is an aliphatic group, saturated or unsaturated, linear or branched,
having from 6 to 20 atoms of carbon, preferably from 8 to 16 atoms of carbon;
G is a residue of a reducing saccharide, preferably of glucose, connected to Rxe2x80x94O by means of an ethereal O-glycosidical bond;
O is an oxygen atom;
D is an acyl residue of sulfosuccinic acid or of a carboxylic acid selected from the group consisting of citric, tartaric, maleic and malic acid.
n is a number between 1 and mxe2x88x921, where m is the number of carboxylic groups in the acid that originates D;
x is a number from 1 to 10, representing the average degree of oligomerization of G;
y is a number from 1 to 10 representing the degree of average esterification of (G)x.
According to a fundamental aspect of the present invention, the aqueous surfactant composition containing from about 10% to 60% by weight of a mixture of surfactants is directly prepared by
a) reacting at 110-130xc2x0 C. for about 2-3 hours a reducing saccharide, preferably glucose, with a fatty alcohol, the alcohol being in a molar excess of from 2 to 5 folds;
b) distilling off from the reaction mixture part of the unreacted fatty alcohol thus obtaining a mixture of alkylpolyglycoside and fatty alcohol containing from 3% to 15% by weight of fatty alcohol;
c) esterifying the mixture of alkylpolyglycoside and fatty alcohol thus obtained by adding to the reaction mixture at 110-130xc2x0 C. over a period of 15-240 minutes maleic anhydride or a bi- or tri-carboxylic acid selected in the group consisting of citric acid, tartaric acid, maleic acid and malic acid;
d) diluting with water the cooled reaction mixture;
e) if maleic anhydride is used in step c), sulfonating the resulting mixture; or, if citric, tartaric, maleic or malic acid is used in step c), neutralizing the resulting mixture.
The aqueous surfactant composition of the present invention may advantageously comprise glycols, polyglycols or oligoglycols. Examples of glycols, polyglycols and oligoglycols include polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol monomethylether, polypropylene glycol monomethylether, ethylene glycol monomethylether, propylene glycol monomethylether, diethylene glycol monomethylether, dipropylene glycol monomethylether, polyethylene glycol dimethylether, polypropylene glycol dimethylether, ethylene glycol dimethylether, propylene glycol dimethylether, diethylene glycol dimethylether, dipropylene glycol dimethylether. Preferred glycols according to the present invention are ethylene glycol, diethylene glycol or dipropylene glycol.
When considering surfactant compositions used in wellbore cleaning operations, particularly important is their toxicity to aquatic organisms, especially those low in the food chain, because of the possibility of accidental or willful discharge into the marine environment of the cleaning compositions, or of fluids contaminated with the cleaning compositions. For this reason, diagnostic toxicity testing of the aqueous surfactant compositions of the present invention were performed on the salt water crustacean, Artemia Salina. The aqueous surfactant compositions of the present invention exhibit an excellent cleaning performance while showing a clear eco-toxicological advantage over conventional compositions.
Cleaning agents, for oil and gas well use, are generally commercially supplied as relatively concentrated products and are normally diluted with locally available water before use. In the preferred embodiments of the invention, the aqueous surfactant compositions are diluted at from 1 to 10% by weight in viscosified water. The water may be hard or soft, or may very rarely be sea water when the supply of fresh water is severely limited.
Cleaning agents must meet specific performance requirements, specifically in terms of cleaning ability, compatibility with other substances used in the cleaning system and compliance with environmental legislation. The compositions of the present invention may also be applied in pipeline cleaning or pigging operations, for gravel pack or fracture cleaning fluids for wells, in spacer fluids, corrosion inhibitor fluids, wetting agents for cement slurries, as well as foaming agents and in other cleaning operations which are associated with hydrocarbon production and transport. These compositions are most useful for wellbore cleanout operations when the salinity and temperature involved with cleanout will not result in degradation of the composition or loss of its effectiveness.
The fluid remaining in a wellbore after completion of the drilling and casing process may well contain a significant amount of brine. Thus any cleaning solution used should be stable over a relatively wide range of temperatures, be tolerant of both caustic and acidic fluid compositions, and be tolerant over a relatively wide range of fluid salinity. The aqueous surfactant compositions in accordance with the present invention exhibit these properties in the conditions used in field applications.
It is known to those skilled in the art that cleaning regimes where a cleaning agent flows over a surface to be cleaned can be divided into laminar flow or turbulent flow regimes, where turbulent flow usually has an advantage of increasing the cleaning efficiency. To promote a turbulent flow regime, those skilled in the art often will use the cleaning agents, which are commercially supplied as concentrated products, and dilute them with locally available fresh water, which is viscosified by addition of commercial grades of suitable polysaccharide-based, or other, viscosifiers.
In a particular embodiment of the invention, it is generally preferred to add the present surfactant mixture to water viscosified with a natural polysaccharide, such as xanthan gum, in order to obtain a viscous aqueous composition suitable for cleaning under turbulent flow conditions.
The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.